1. Field of the Invention
The present invention relates to stuffing boxes for reciprocating pumping units having packing seals through which a polish rod reciprocates in a sealed relationship. In particular, the present invention relates to arrangements for minimizing and compensating for wearing of the packing seals in such stuffing boxes, especially in the oil well pumping context.
2. Description of Related Art
Typically, oilfield pumping units have a stuffing box through which a polish rod reciprocates in a sealed relationship and to which a string of sucker rods is connected for operating a downhole pump. The stuffing box seals wear with usage and must be replaced before they wear to the point that crude oil leaks from the stuffing box contaminating the surroundings. Stuffing box seal wear can result from a number of factors such as misalignment of the polish rod, friction between the rod and packing and the effects of particle buildup in the area underneath the packing. In the past, some packing had to be changed as frequently as every day and rarely longer than every two weeks. Thus, significant savings can be had if the life of the stuffing box packing could be significantly extended.
Thus, various techniques have been developed in an attempt to extend stuffing box packing life by minimizing wear-inducing factors. For example, U.S. Pat. No. 3,395,923 discloses a self-lubricating stuffing box in which an oil reservoir receives a small portion of the oil being pumped so as to maintain an oil layer between the packing rings. However, abrasives are still free to collect below the packing unit where they can score and frictional wear the polish rod and be drawn up into the packing.
U.S. Pat. Nos. 5,636,688 and 5,343,944 show self aligning stuffing boxes having a seal assembly which is able to move radially within the main body of the stuffing box to align the polish rod with the production tubing of the wellhead. However, the o-ring seals on the movable end surfaces present their own potential failure site. More importantly, because this arrangement only permits seal assembly which is able to move radially within the main body of the stuffing box to align the polish rod the problem of rubbing between the polish rod and the packing seals and/or on the stuffing box still exists.
It has also been known to use gas pressure built up in the tubing of an oil well as a force acting to compress the packing in a stuffing box; see, U.S. Pat. No. 1,959,984. However, no provision was made control the pressure applied to the packing, and in particular, because there was no mechanism for amplification of the applied pressure in any manner, packing utilization could not be optimized. Moreover, the design of the seal arrangement of this patent, in which wedge-shaped seals are repeated stressed and relaxed, itself contributes to wearing of the seals as the wedge-shaped seals are rubbed against each other.
Thus, there is still a need for an effective means for preventing premature wearing of packing seals due to misalignment, inadequate or improper pressurization of the seals, and the effects of debris accumulations so that the packing seals will not have to be changed as often as is currently the case and so as to minimize the danger of leakage into the environment.
It is a primary object of the present invention to provide a stuffing box with a pressure compensated packing which will insure that the seals are always properly adjusted.
It is a further object of the present invention to prevent shortening of the packing life due to misalignment of the polish rod.
Yet another object of the invention is prevent impregnation of the packing seals and scoring of the polish rod due to debris buildup under the packing.
A still further object of the invention is enable the foregoing objects to be achieved in a manner which does not require a substantially new type of stuffing box but rather will be amenable to implementation on existing types of stuffing boxes via relatively minor modifications.
These objects and others are achieved in accordance with the present invention by the implementation of a pressure amplification feature by which tubing pressure is amplified in an appropriate ratio and applied to the packing seals to insure that they are correctly compressed at all times without producing a binding of the packing seals with the polish rod. Furthermore, the stuffing box is mounted to the well head in a manner which permits a floating self-alignment upon loosening of a few bolts. Still further, a venturi connection is provided which flushes the underside of the packing area so as to keep it free and clear of debris buildup.
Other objects and features of the invention will become apparent from the following detailed description when viewed in conjunction with the accompanying drawing.